Need help identifying the source of a bad smell in the bathroom

[MChamp]

I've got a musty, stale smell coming from the downstairs powder room in my house and can't seem to identify the source. I first noticed the smell in summer of last year but it wasn't too bad, just caught a whiff of something every once in a while when walking by the room. After it didn't go away for a while, I did some troubleshooting to try to figure out it and wasn't able to identify the source. The smell eventually faded away almost entirely, so I stopped worrying about it. However, over the last few days it's come back with a vengeance, and now I really need to figure out where it's coming from so I can take care of it.

The room is a small powder room, about 5'x5' with a toilet and a sink. There is no window, but has a ceiling exhaust fan and a floor HVAC vent. Floors are hard wood, with crawl space below. There's a bedroom directly above, and it's surrounded on all sides by the kitchen, pantry, office, and hallway. None of the adjoining rooms have any smell. When I leave the door to the bathroom closed for a while then open it, the scent is a lot worse, so I know it's coming from the bathroom. I can't identify a specific place the smell is coming from when I try to sniff individual parts of the bathroom, it's kind of diffuse throughout. It sorta smells like sewer gas, but I'm not expert on the small.

Things I have done to evaluate this so far that have not fixed the problem:
-Cleaned the floors, walls, and fixtures in the bathroom thoroughly
-Checked the sink p-trap for leaks, made sure it's holding water (it is)
-Pulled up the toilet and replaced the wax ring
-Sealed off the floor vent with plastic sheeting/tape
-Pulled all of the insulation down from below the floor in the crawlspace, found some mice droppings but no dead animals

I had a plumber come out way back when it first started after the above didn't get me an answer. He couldn't smell anything at the time, but the scent had mostly resolved by then. He did a quick inspection of the pipes in the crawlspace and didn't find anything.

We have had some problems with mice, so I worry about a dead rodent in the walls or below the floor, but I didn't find anything in the crawl space and it doesn't really smell bad when I'm down there. If there was something dead in the walls, I would think I would be able to smell it from one of the adjoining rooms. I sealed off the vent to see if maybe there was something dead in the HVAC system that was blowing the smell into the room, but that didn't change anything.

Pretty often when the sinks are draining from anywhere in the house I hear that "glug, glug" sound of water not draining smoothly, but it's delayed by several seconds after shutting off the water and sounds like it's coming from a distance rather than the p-trap directly below the sink.

We have had problems with squirrels/birds nesting in our chimney - I wonder if they might be in our sewage vent pipes as well? Could obstruction of the vent pipe cause such a problem? Would I expect to have problems in other rooms as well if the vent pipes were a problem?

I feel like it's coming from the toilet, but I could certainly be wrong. Can smells come up from the sewer pipe below even if the toilet is well sealed and the bowl is full of water?

I might have to call the plumber out again now that the smell is back and stronger, but I was hoping I might get some guidance on where the problem might be before I do that so that it might be a more useful visit this time.

Thanks!

 

[Plumber69]

I've got a musty, stale smell coming from the downstairs powder room in my house and can't seem to identify the source. I first noticed the smell in summer of last year but it wasn't too bad, just caught a whiff of something every once in a while when walking by the room. After it didn't go away for a while, I did some troubleshooting to try to figure out it and wasn't able to identify the source. The smell eventually faded away almost entirely, so I stopped worrying about it. However, over the last few days it's come back with a vengeance, and now I really need to figure out where it's coming from so I can take care of it.

The room is a small powder room, about 5'x5' with a toilet and a sink. There is no window, but has a ceiling exhaust fan and a floor HVAC vent. Floors are hard wood, with crawl space below. There's a bedroom directly above, and it's surrounded on all sides by the kitchen, pantry, office, and hallway. None of the adjoining rooms have any smell. When I leave the door to the bathroom closed for a while then open it, the scent is a lot worse, so I know it's coming from the bathroom. I can't identify a specific place the smell is coming from when I try to sniff individual parts of the bathroom, it's kind of diffuse throughout. It sorta smells like sewer gas, but I'm not expert on the small.

Things I have done to evaluate this so far that have not fixed the problem:
-Cleaned the floors, walls, and fixtures in the bathroom thoroughly
-Checked the sink p-trap for leaks, made sure it's holding water (it is)
-Pulled up the toilet and replaced the wax ring
-Sealed off the floor vent with plastic sheeting/tape
-Pulled all of the insulation down from below the floor in the crawlspace, found some mice droppings but no dead animals

I had a plumber come out way back when it first started after the above didn't get me an answer. He couldn't smell anything at the time, but the scent had mostly resolved by then. He did a quick inspection of the pipes in the crawlspace and didn't find anything.

We have had some problems with mice, so I worry about a dead rodent in the walls or below the floor, but I didn't find anything in the crawl space and it doesn't really smell bad when I'm down there. If there was something dead in the walls, I would think I would be able to smell it from one of the adjoining rooms. I sealed off the vent to see if maybe there was something dead in the HVAC system that was blowing the smell into the room, but that didn't change anything.

Pretty often when the sinks are draining from anywhere in the house I hear that "glug, glug" sound of water not draining smoothly, but it's delayed by several seconds after shutting off the water and sounds like it's coming from a distance rather than the p-trap directly below the sink.

We have had problems with squirrels/birds nesting in our chimney - I wonder if they might be in our sewage vent pipes as well? Could obstruction of the vent pipe cause such a problem? Would I expect to have problems in other rooms as well if the vent pipes were a problem?

I feel like it's coming from the toilet, but I could certainly be wrong. Can smells come up from the sewer pipe below even if the toilet is well sealed and the bowl is full of water?

I might have to call the plumber out again now that the smell is back and stronger, but I was hoping I might get some guidance on where the problem might be before I do that so that it might be a more useful visit this time.

Thanks!

Probably your sink ptrap is siphoning out. Too know for sure... tape over the drain and overflow and dont use it for a week. If smell is gone thats your problem

 

[Sponsor]

 

[Reach4]

You might find this of interest:
https://terrylove.com/forums/index.php?threads/water-in-toilet-bowl-smell.70924/


Isolate the toilet and lavatory with cheap plastic drop cloths. See if the smell is from the under-side of each the plastic drop cloth.

 

[MChamp]

Probably your sink ptrap is siphoning out. Too know for sure... tape over the drain and overflow and dont use it for a week. If smell is gone thats your problem

Ok I'll give that a try. What's the reason I need to wait a whole week?
What would cause a p-trap to siphon out? And wouldn't I expect the p-trap to be empty if that were happening? It looks like it has water in it when I look from above, and it definitely had water in it the last time I removed it. The sink typically gets used several times per day, so I would expect it would get filled back up regularly.

 

[MChamp]

You might find this of interest:
https://terrylove.com/forums/index.php?threads/water-in-toilet-bowl-smell.70924/


Isolate the toilet and lavatory with cheap plastic drop cloths. See if the smell is from the under-side of each the plastic drop cloth.

I read that thread, I have plastic seats on all the toilets so I don't think that's the issue.
I can try the plastic wrap and drop cloths, have plenty of those lying around from my various painting projects.

 

[Plumber69]

Ok I'll give that a try. What's the reason I need to wait a whole week?
What would cause a p-trap to siphon out? And wouldn't I expect the p-trap to be empty if that were happening? It looks like it has water in it when I look from above, and it definitely had water in it the last time I removed it. The sink typically gets used several times per day, so I would expect it would get filled back up regularly.

If its not vented, plugged vent, plumbed wrong can cause this. Had a friend with a powder room and same issue. But he had no ptrap. Just try it. If it's not that then its a dead rodent or open vent somewhere

 

[Jeff H Young]

that glug glug sound try tapping off Lav or the plastic sheet over toilet and lav suggested. probebly got a stoppage or improper modifications to plumbing DWV system

 

[Plumber69]

cheater vent may solve your smell.... pic of plumbing under sink

 

[MChamp]

I taped off the sink drain and overflow and sealed the toilet bowel in plastic wrap last night. Scent was just as bad (maybe worse) this morning. So this morning I pulled the toilet again and sealed over the drain pipe with plastic as well. I guess I'll see if the smell gets better in a few hours. After pulling the toilet, the scent coming up from the drain wasn't really the same as the scent I have been smelling, and not nearly as bad.

Here's the pic of below the sink plumbing as requested.

 

[Stefaan]

I taped off the sink drain and overflow and sealed the toilet bowel in plastic wrap last night. Scent was just as bad (maybe worse) this morning. So this morning I pulled the toilet again and sealed over the drain pipe with plastic as well. I guess I'll see if the smell gets better in a few hours. After pulling the toilet, the scent coming up from the drain wasn't really the same as the scent I have been smelling, and not nearly as bad.

Here's the pic of below the sink plumbing as requested.
View attachment 70172
View attachment 70173
View attachment 70174

Did you ever figure this out? I'm having a very similar issue and it's been about a month now. Almost positive it's not plumbing related but the smell is not fading (like a decomposing mouse would).